Clinton's trip to California next month is expected to include an event in predominantly Latino East Los Angeles as well as a high-dollar fundraiser.

While the endorsement of a former president is big news in any state, the former chairman of the California Democratic Party thinks it could be especially significant in California, a state where Clinton has had a strong following ever since he beat Brown in the state's 1992 presidential primary.

"There has never been a former president who has endorsed a candidate in a primary for statewide office in California," said Art Torres, a former state lawmaker who headed the California Democratic Party from 1995 until earlier this year but is neutral in the current race.

"In 1992, Bill Clinton beat Jerry Brown in California by 7 points. He then beat Bush by 13 points in the general," Torres said. "And then in last year's presidential campaign, Hillary [Clinton] beat Obama by 9 points including a 67-to-32 margin among Latinos."

Newsom Hoping Clinton Will Garner Latino Votes

In addition to helping with fundraising and Latinos, the Newsom campaign is hoping that Clinton's endorsement can help the San Francisco mayor make inroads in Southern California.

When Clinton ran against Brown in 1992, the future president carried 43 of the state's 58 counties, including Los Angeles County.

"California is still Clinton country in many ways," said state Sen. Alex Padilla, the chairman of Newsom's campaign. "We are proud supporters of Barack Obama, but we have not forgotten what the Clintons did for California."

The door to a Clinton endorsement in a competitive primary was opened earlier this year when Los Angeles Mayor Antonio Villaraigosa announced that he would not be a candidate for governor.

At the time of the Villaraigosa announcement, pundits were unsure which Democratic candidate would benefit.

The Clinton endorsement is a sign that Villaraigosa's exit might ultimately prove to be more helpful to Newsom than to Brown, since the former president would not have been able to endorse the San Francisco mayor if Villaraigosa, another top backer of his wife's presidential campaign, were also in the race.

Brown was neutral in the 2008 Democratic presidential primary.

"Jerry Brown is still very much the candidate to beat and has run a great campaign to date," said former Clinton adviser Chris Lehane. "But in the world of endorsements, this is certainly one of the real 'gets' that can translate into something. The Clinton name is still golden in the Golden State."

If the Brown campaign portrays the Clinton endorsement as lingering sour grapes over the 1992 campaign, Lehane said he thinks it could backfire.

"Bill Clinton is one of the most popular Democrats in California," Lehane said. "The last thing in the world you would want to do is inject some conflict into this endorsement, because it would just get it out there in a bigger way."

Former President on a 'Payback Tour'?

"When you're dealing with one of the most popular people in the party, the more that people hear about him endorsing your opponent, the less good it is," he said.

While California has never in recent memory seen a former president intervene in a competitive statewide primary, Bill Clinton has already done it in two other 2010 races including Rep. Kendrick Meek's, D-Fla., Florida Senate race and Lt. Gov. Lee Fisher's Ohio Senate race.

Given the efforts that Clinton is making on behalf of several of his wife's backers around the country, the Brown camp may try to dismiss Clinton's endorsement as simply the latest obligatory stop on the former president's "payback tour."

Tulchin said, however, that the Clinton endorsement cannot be dismissed so easily.

"Clinton could have easily taken a pass," Tulchin said. "The fact that he is coming out now is a bold move."

The key going forward, according to Tulchin, is just how big of an investment Clinton makes in this race.

"For Gavin to benefit from this fully, he needs significant help raising money," Tulchin said. "If Clinton can help Gavin raise money, then Clinton gives Gavin the resources he needs to sell his story."